This invention relates to hydraulic steering systems for marine craft, and more particularly for marine craft having outboard drives or inboard/outboard drives.
Smaller marine craft are typically powered by outboard drive units or inboard/outboard drive units which are mounted on the transom of the marine craft at the stern. The drive units can be tilted upwards about a horizontal axis of rotation for storage purposes, in shallow water, to perform maintenance operations or for other such purposes. The drive unit is usually mounted on a swivel bracket which allows the drive unit to be tilted upwards. The drive units can be rotated about a steering axis relative to the swivel bracket.
In some such marine craft, a hydraulic steering system is provided in order to rotate the drive unit about the steering axis. Various systems have been developed in the past which permit the drive units to be tilted upwards when so equipped with hydraulic steering systems.
For example, U.S. Pat. No. 6,276,771 to Treinen et al. discloses an integrated hydraulic steering actuator where the tilt bracket has a cylindrical portion. A hydraulic actuator, comprising a cylinder member and a piston member, are disposed within the cylindrical portion of the tilt bracket. However this arrangement has a number of disadvantages. For example, the assembly has a relatively large number of parts. The tilt bracket has a cylindrical portion with a cylindrical bore. Both an inner cylinder and an outer cylinder are disposed within the bore. A piston of a piston and piston rod assembly is reciprocatingly and slidingly received within the inner cylinder. The relatively large number parts increases to the cost of components as well as the assembly time and accordingly may increase the cost of the overall system. Furthermore, where different metals are used for the various components, such as the inner cylinder, the outer cylinder and the cylindrical portion of the tilt bracket, corrosion problems can result in a marine environment.
Accordingly is an object of the invention to provide an improved hydraulic steering system for marine craft having stern drives, where non-rotational travel of the hydraulic actuator is effectively eliminated when the stern drive is tilted, but which offers simpler construction and requires fewer parts than the prior art.
It is another object of the invention to provide an improved hydraulic steering system for marine craft where non-rotational travel of the hydraulic actuator is effectively eliminated when the stern drive is tilted, but which does not acquire a separate hydraulic cylinder, apart from the swivel bracket, to support the pivotal connection between the swivel bracket and the transom bracket.
Is further object of the invention to provide an improved hydraulic steering system for marine craft where non-rotational travel of the hydraulic actuator is effectively eliminated when the stern drive is tilted, and where potential corrosion between the steering cylinder and a tilt bracket is eliminated by forming the cylinder as part of the tilt bracket.
According to the invention, there is provided a steering apparatus for marine craft having a stern and a propulsion unit mounted on the stern. The system includes a first bracket which is connectable to the stern of the marine craft. There is a second bracket connectable to the propulsion unit. The second bracket is rotatably connected to the first bracket for relative rotation about an axis of rotation. The propulsion unit can be rotated about the axis of rotation relative to the stern of the craft. The second bracket has a cylindrical bore extending therethrough. A piston is reciprocatingly received within the bore, slidingly engages the bore and has a piston rod connected thereto. The piston rod is operatively connected to the propulsion unit. Preferably the piston rod is coaxial with the axis of rotation.
In one example, the second bracket has an actuator portion. The bore extends through the actuator portion. The second bracket comprises a cylinder for the actuator. The actuator portion may have a cylindrical bushing surface. The first bracket has an extension. The extension has a cylindrical bore rotatably receiving the bushing surface. The bushing surface and the cylindrical bore are co-axial with the axis of rotation.
The invention offers significant advantages over the prior art. It provides a hydraulic steering system for stern drives where there is no arcuate travel of the hydraulic actuator when the stern drive is tilted. At the same time, it significantly reduces the complexity of the mechanism compared to U.S. Pat. No. 6,276,977 because it does not require a separate outer or inner cylinder apart from a bore through the swivel bracket itself. In effect, a portion of the swivel bracket becomes the cylinder of the actuator.
Nor is it feasible to readily modify the above U.S. patent to delete the inner and outer cylinders. This is because the extensions to the clamp brackets are beside the cylindrical portion of the swivel bracket which therefore does not present a continuous cylindrical bore for a cylinder. Furthermore, the outer cylinder is required in order to act as a pin in the hinged connection between the extensions to the clamp brackets and the cylindrical portion of the swivel bracket.
Corrosion cannot occur between the hydraulic cylinder and the tilt bracket according to the invention because they comprise a single component in the preferred embodiment.